The problem of providing automatic furling for sailing vessels has long plagued the sailing industry. In recent year various improvements have been made. For example, head sails in fore-and-aft rigged ships are now being "roller reefed" or furled by mounting them on a cable which is adapted with swivels above and below the sail so that the sail can be wound up on the cable by rotating it. Main sails are also being "roller reefed" by mounting them on a rotatable boom. Furling or reefing is accomplished with these later equipments by rotating the boom while lowering the sail (see e.g. U.S. Pat. No. 3,285,215). For square sail rigged ships, an arrangement has been proposed for employing a slotted hollow mast and drawing the sail into the hollow by winding it up on a rotatable cylindrical tube located within the mast (see U.S. Pat. No. 3,483,840). It has also been suggested that reefing or furling can be done in small boats having unstayed masts, by rotating the mast (see U.S. Pat. No. 2,107,303). A recently developed form of reefing and furling of main sails comprises providing an aft-facing slot in a hollow mast, and securing the sail to a rotatable cable in the hollow within the mast which cable employs swivels at the peak and tack and is virtually identical to the rotatable cable described above for use with head sails.
These prior art uses and suggestions leave much to be desired. Roller reefing of head sails on a rotatable cable, although widely used, has problems. The cable is flexible and as a consequence it yields torsionally. This means that it is not well suited for reefing, i.e. sails while partly furled. This becomes more of a problem as the wind force and hence the need for it increases. Roller reefing of head sails is, therefore, best suited for completely furling, or in effect, storing the head sail.
Roller reefing of main sails (or similar sails abaft the main mast) on a rotating boom has other disadvantages. Since the sail must be wound up on the boom, the reinforcing cable on the luff of the sail (as well as the slides when applicable) must also be wound on the boom. This causes a bunching and increased diameter at the tack, and the sail is then drawn onto the boom unevenly and wrinkles, extending upwardly across the sail result. In addition, the reefing operation requires coordination between the rolling and the sail lowering steps, which coordination requires extra hands, and can be embarrassing especially in a critical moment when it suddenly becomes necessary to reef, a moment when the extra hands are most apt to be needed elsewhere.
The proposals of U.S. Pat. Nos. 2,107,303 and 3,483,840 mentioned above also involve a variety of disadvantages, but since they are not relevant to the type of rig of the present invention their disadvantages are likewise not relevant.
The reefing and furling of U.S. Pat. No. 3,835,804 is particularly relevant to the present invention because it involves drawing a fore-and-aft or Bermudian rigged main sail into a hollow mast which supports the luff of the sail. The arrangement of U.S. Pat. No. 3,835,804, however, has several significant draw-backs as follows. First, the rotating cable inside the mast, to which the luff of the sail is attached, must have freely rotating swivels at the top and bottom. Swivels operate well if they are properly oiled and maintained, but they can become fouled, clogged, or corroded. This is particularly a problem with the swivel at the peak, where maintenance is not easy. Another problem relates to the flexibility of the cable. It twists torsionally. This is accentuated not only when the peak swivel is sticking, but also when the wind force and hence the force needed to haul in the sail, increases. When the cable twists, the sail winds up more on the lower part than above and wrinkles appear as a result. Wrinkles are particularly vexatious with this rig because the aft-facing slot must be quite narrow in order to keep the sail from pulling the cable through the slot, and wrinkles tend to jam in the slot. Again, as the wind force increases, the sail pulls the cable toward the slot with greater force thereby offering greater resistance to winding, greater torsional bending and more wrinkles, at the critical moment of increased need for reefing--exactly when wrinkles and jamming are most vexatious. Another factor also causes wrinkling. Most main sails are cut with a roach along the luff to provide "fullness" for the sail. Generally speaking more fullness is desired for light air, whereas flatter sails are desired for heavy air. It is usual, however, to provide an average fullness, so that the sail will be useful for a wide range of wind forces. When such a sail is being reefed or furled with the arrangement of U.S. Pat. No. 3,835,804, since the rotating cable is relatively straight and the sail luff is curved, there is no place for the extra material to go. It simply wrinkles. As a result of these disadvantages of the arrangement of U.S. Pat. No. 3,835,804, the users are given elaborate instructions on how to cope with jamming of the sail in the slot involving emphasis on care for the maintenance of the swivels, techniques of heading into the wind to relieve tension on the sail together with repeated short cycles of furling and unfurling to loosen jams. Another recommendation is to have the sails cut very flat. Cutting the sails flat, of course, helps avoid wrinkles, but is not good for sailing efficiency.